1. Field of the Invention
The present invention relates to a digital television broadcast signal receiver to receive digital television broadcast signals, such as ATSC (Advanced Television Systems Committee).
2. Description of the Related Art
Since, in North America where the ATSC digital television broadcast (TV broadcast) is provided, large cities are located in plain fields, and TV broadcast signals come from various directions from the viewpoint of users who receive TV broadcast signals sent from around each city, users need to adjust the direction of antennas towards the broadcast station which broadcasts programs they wish to watch. Therefore, a multi-directional antenna is coming into practical use. A general antenna for ground wave television broadcasts has a shape called a Yagi antenna and is characterized by the ability to receive even weak radio waves because of strong directional characteristics. On the other hand, it also has a disadvantage in that it can receive only radio waves from a given broadcast station because of these strong directional characteristics. At the same time, the strength of receiving signals varies even with slight direction changes because of these characteristics.
Also, for devices to control the directional characteristics of antennas, the following method (see Japanese Unexamined Patent Application Publication H06-334931) is known: adjusting the directional characteristics of antennas by phase combinations through shifting with a switch by using different received radio wave phases of two types of antennas; in addition, for devices relating to the automatic synchronization reception, the following auto-preset method (see Japanese Unexamined Patent Application Publication H08-242144) is known: automatically storing receiving frequency information into a memory by supplying power when an antenna is connected to a tuner.
As described above, since there is a possibility of broadcast radio waves coming from all directions in the ATSC digital television broadcast in the US, a multi-directional antenna (smart antenna) is required to receive TV broadcasts, and, in the ETA-909 specification, a smart antenna is specified to have receiving directions in each of 16 directions into which a circle is divided. Meanwhile, as a digital television broadcast signal receiver that receives TV broadcast signals, it is set to be adjustable for the receiving direction of a multi-directional antenna for all 16 directions in order to comply with the EIA-909 specification.
In addition, there are some digital television broadcast signal receivers (digital TV broadcast signal receiver) that are equipped with an auto-scan function to select the antenna direction that can best receive TV broadcast signals of channels selected by a user. The receiving direction can be set by scanning all 16 directions for each channel and selecting the direction with the best reception conditions for it because the locations of broadcast station's antennas, which are broadcast towers, usually do not change. However, in countries like the U.S., broadcast stations, which are relatively easily to start as a new business, often go bankrupt. Therefore, a channel that could not be received before may become newly receivable, or one that could be received before may become unreceivable. Moreover, the reception condition of TV broadcast signals may vary due to the construction of tall buildings. Consequently, resetting may be needed as required for the best receiving direction of channels selected by a user. Even in the case in which a multi-directional antenna that requires less time to switch the receiving direction is connected to a digital TV broadcast signal receiver equipped with the auto-scan function, since the interval to output control signals for switching the receiving direction is long, the time required to determine the best receiving direction of the TV broadcast signals of a selected channel becomes very long, which irritates users.
On the other hand, in the initial direction setting of a smart antenna, some time is spent to measure the best receiving direction and the maximum signal receiving level for all local channels and for all directions in advance, they are stored in a TV receiver built-in memory, and the direction of the antenna is set to be able to be adjusted to a desired channel quickly based on the stored data when accessing for channel selection. However, since, in the case of using an in door antenna, there is a possibility that a user might change the installation location of an antenna or accidentally change the direction of an installed antenna physically, trouble such as TV signals becoming unreceivable can easily occur. In this case, once the direction of the antenna changes, the direction data stored in the TV receiver is thrown out, and the receiving direction data for each channel stored in the memory becomes irrelevant.
Therefore, in order to return to normal reception, the antenna search must be started again from the beginning to repeat the receiving level measurement for all channels and for all directions. For this, it is first necessary to detect the antenna movement as soon as possible and adjust the direction. When signals cannot be received on Channel X, there is a problem: even though the directions of antennas are not actually misaligned, some time is wasted on meaningless operations, such as unnecessary scanning of all channels, if there is no response to determine whether only Channel X becomes unreceivable for some reason or whether there is a misalignment of all antenna directions.
In addition, when the antenna direction is reset, there is a problem: since the stored direction information includes receiving direction information, receiving signal strength information, and additional information (such as the ADD flag, showing that the receiving signal strength is higher than the standard level), and the direction of an antenna is controlled according to the stored information, the correct antenna direction control is interfered with, as in a disruption of antenna direction adjustment in which the correct direction cannot be set, if old direction information is left without being updated.